A crosshead connects a straight piston rod to a swinging connecting rod. Its shoes run in fixed guides, transferring the connecting rod’s transverse force into the frame while keeping the piston rod on the cylinder axis.
Cross-Head Slide Interactive Calculator
Set axial force, maximum rod inclination and the number of equally loaded guide surfaces. Follow the piston, crosshead and crank while comparing live and peak static forces.
Equation Used
- Constant axial force; quasi-static balance.
- No inertia, friction, clearance or bearing-pressure calculation.
- Entered guide count refers only to simultaneously loaded surfaces with equal sharing.
- Illustrative lengths; r/L=sinθmax sets animation geometry.
- Actual engine force cycle and manufacturing dimensions are outside this model.
Cards show maximum-angle values under constant axial force; live pose values appear in the drawing.
Keep the piston rod straight
The sectioned cylinder contains the piston. Its rod connects to the guided crosshead, and a separate connecting rod joins the crosshead pin to the crank pin. The crankshaft bearing and the slide guides are supported on the frame.
The animation solves the slider-crank geometry with a constant connecting-rod length. Its illustrative crank radius is chosen so the maximum rod angle equals the entered value. Guide-reaction direction reverses as the rod crosses the piston axis. The highlighted shoe is the loaded side in the shown constant-force model.
A guided force connection
Crossheads occur in reciprocating engines and compressors. Their function is to guide linear motion and carry the connecting rod’s transverse component. This calculator studies the ideal force balance; it does not rate a particular engine, crosshead bearing or guide design.
Resolve the connecting-rod force
Let F be the piston-axis force and θ the connecting rod angle to that axis. Ignoring inertia and friction, axial equilibrium gives rod force R=F/cosθ. Transverse equilibrium then requires guide reaction G=|R sinθ|=|F tanθ|.
The entered angle is the maximum inclination used in the illustrative cycle. The result cards report the corresponding peak values for constant F. The drawing separately reports the instantaneous angle and forces. The side-to-axial ratio is 100|tanθ| percent.
If n surfaces are actually loaded together and share equally, each carries G/n. Enter the number of those loaded surfaces. Counting all installed guide bars, including unloaded opposing faces, would understate the contact load.
Example at 5.7 degrees
With a 50 kN axial force and maximum rod angle of 5.7 degrees, peak side thrust is about 4.99 kN and peak connecting-rod force about 50.25 kN. Two equally loaded surfaces would each carry about 2.50 kN.
At zero inclination the guide reaction is zero and rod force equals axial force. A larger number of sharing surfaces changes only the ideal per-surface result; it does not reduce total side thrust.
Limits of this static model
Piston force is constant here. A real engine’s gas force and inertia vary with crank position, so its peak guide reaction need not occur at the maximum rod angle. Guide friction, clearance, impact, bearing pressure and structural deflection are not evaluated.
The drawing uses illustrative lengths and does not supply stroke, machining tolerances, lubrication settings or service limits. Equal sharing must be supported by the actual arrangement. Unequal stiffness, clearance and wear can concentrate load.
Crosshead questions
Why do the result cards stay fixed while the animation moves?
The cards show the selected maximum-angle force comparison. The animation has separate live values for its current rod angle.
Should I count both opposing guide faces?
Only count surfaces simultaneously carrying and sharing the same reaction. An unloaded opposing face does not reduce the load on the loaded face.
Why does the mechanism stop moving at zero angle?
The illustrative radius-to-rod ratio becomes zero. This limiting geometry has no side thrust and no stroke.
Is the result a bearing-pressure check?
No. Contact area and bearing design are not inputs.
References
Wärtsilä: Crosshead, for the crosshead’s role in carrying transverse load away from the piston.
Wärtsilä Encyclopedia of Ship Technology, printed page 152: crosshead and connecting-rod photograph and definition. The equations here follow ideal axial and transverse force equilibrium.
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